Approaches to studies on neuronal glial relationships by C-13-MRS analysis

The use of different C-13-labelled precursors alone or in combination ([1-C-13]glucose, [2-C-13]glucose, [1-C-13]acetate, [2-C-13]acetate and [1,2-C-13(2)]acetate) to study neuronal/glial metabolic relationships by MRS is discussed, Glutamine and citrate resonances represent glial metabolism if a combination of [1-C-13]glucose + [2-C-13]acetate is used, but only for short time periods. A combination of [2-C-13]glucose + [2-C-13]acetate will label -COO- groups from glucose and -CH2 groups from acetate, respectively, which distinguish well in theory. However, this approach is severely limited by the long T(1)s of -COO- groups and low S/N. Contributions of the anaplerotic pathway can be assessed using [2-C-13]glucose, but again can be limited by the long T(1)s of -COO- groups. Labelling of glycerol-3-phosphate (believed to be produced in glia) from [1-C-13]glucose is difficult to see under normal conditions but has proved useful in, e,g., hypoxia, We believe the most promising approach is the use of [1-C-13] glucose with [1,2-C-13(2)]acetate, by analysis of the multiplets ('isotopomers') of the amino acid resonances.